According to a recent study published in the journal PLOS One, being overweight within the body mass index (BMI) range does not necessarily lead to a higher risk of death. This research adds to the growing body of evidence suggesting that BMI alone is not an accurate indicator of an individual’s overall health.
The study analyzed data from over 550,000 adults in the United States, spanning an average period of nine years, to examine the relationship between BMI and the risk of death from any cause. The findings revealed that there was no significant increase in the risk of death for individuals aged 65 and above whose BMIs ranged from 22.5 to 34.9.
Similarly, younger adults with BMIs between 22.5 and 27.4 did not exhibit a significant increase in mortality risk, as per a report by NBC News. It’s important to note that a BMI of 25 or higher is considered overweight, while a BMI of 30 or higher is classified as obesity.
What is a BMI?
As per Medical News Today, for over a century, health professionals have relied on the body mass index (BMI) as a tool to assess whether individuals are underweight or overweight. The recommended BMI range by health experts typically falls between 18.5 and 24.99.
The concept of BMI was developed by Lambert Adolphe Jacques Quetelet, a Belgian astronomer, mathematician, statistician, and sociologist, in the 1830s. It involves a straightforward mathematical formula.
BMI is widely used by researchers in population studies, doctors, personal trainers, and other professionals in their respective fields. But despite its widespread use, BMI has several notable limitations, as per reports. One of its shortcomings is that it fails to account for the distribution of fat and lean tissue (such as muscle) within the body.
How is BMI Calculated?
The calculation of BMI aims to provide an estimation of whether an individual has a healthy weight by dividing their weight in kilograms (kg) by the square of their height in meters (m).
The current calculation for BMI involves dividing a person’s weight by the square of their height:
BMI = weight (kg) / height^2
Accepted criteria for BMI classifications worldwide typically include the following ranges:
- A BMI of 18.49 or below indicates that a person is underweight.
- A BMI between 18.5 and 24.99 suggests that a person has a normal weight.
- A BMI between 25 and 29.99 indicates that a person is overweight.
- A BMI between 30 and 39.99 or higher signifies obesity.
- A BMI of 40 or above indicates morbid obesity.
These BMI ranges serve as general guidelines to assess an individual’s weight status and potential health risks associated with weight.
What Did the Study Say?
As per NBC News, healthcare professionals have criticized the use of BMI for decades, pointing out that it fails to account for important factors such as body fat percentage and variations in disease risk based on race and gender.
Recently, the American Medical Association recommended the use of additional measures, including waist circumference, body fat distribution, and genetic factors, to assess a patient’s health.
The findings of the study mentioned support these new guidelines. Dr. Aayush Visaria, a co-author of the study, stated that their results confirm the poor predictive value of BMI as a standalone indicator of health risk. Waist circumference, on the other hand, showed a stronger association with overall mortality risk. Even among individuals with the same BMI, those with larger waist circumferences faced a higher risk of death.
The study did find that participants with a BMI of 30 or higher had a greater mortality risk. Among younger adults, a BMI between 27.5 and 29.9 was also associated with a nearly 20% higher risk.
Dr. Fatima Stanford, an obesity medicine specialist, highlighted that BMI often equates leanness with health while overlooking other essential factors. She emphasized that substance abuse disorders, tobacco use, and disordered eating can lead to a lean physique but do not indicate good health.
Previous research has also revealed the limitations of using BMI as a sole indicator of obesity or risk of weight-related diseases. Studies have shown that a significant portion of individuals classified as overweight or obese by BMI are metabolically healthy, while a substantial percentage of those with “normal” weights exhibit metabolic health issues.
Any Limitations in the Study?
The new study acknowledged that previous research linking BMI and higher mortality mainly relied on data from the 1960s to 1990s, which predominantly included white participants. However, the demographic composition of the United States has significantly changed since then, with a lower proportion of non-Hispanic white individuals. The new study sought to address this by including a diverse sample of participants, with 69% white, 12% Black, 14% Hispanic, and nearly 5% Asian individuals, which is considered a fairly representative sample.
Dr. Jaime Almandoz, who was not involved in the research, pointed out some limitations of the study. One limitation is that it focuses solely on the relationship between BMI and the risk of death, overlooking other health factors and conditions. Almandoz emphasized that life encompasses more than just mortality and that individuals with higher BMIs may still face health risks such as Type 2 diabetes, increased risk of heart attack, stroke, and heart failure, NBC News reported.
According to the Centers for Disease Control and Prevention (CDC), individuals with BMIs of 25 or higher are at an increased risk of high blood pressure, high cholesterol, Type 2 diabetes, and certain types of cancer.
Almandoz also noted that the study underrepresents the proportion of individuals with obesity. While the study reported that about 27% of the participants had a BMI greater than 30, CDC surveys estimate that 42% of U.S. adults have obesity. The study’s co-author, Dr. Aayush Visaria, acknowledged that if the study had examined participants’ body fat percentages, the prevalence of obesity might have been higher than indicated by BMI alone. This highlights the limitation of BMI in measuring body fat accurately.
Visaria suggested that clinicians should consider using alternative measures of body fat to diagnose obesity, rather than relying solely on BMI. He believes that in the future, such measures will become more commonplace in clinical practice.
